Systems Integration / Power Supplies

Power Supplies Get In On The Reliability Act

The Demand for Increased Reliability and Global Application for Process Control Is Driving Evolution of Power Supply Design

By Jim Montague

Just as large electricity producers and consumers are using smart devices and software to improve power quality and operating efficiency, developers of device-level power supplies are employing many of the same strategies.

Mike Garrick, power supply manager at Phoenix Contact, reports that demand for increased reliability and global application for process control is driving evolution of power supply design. "Process designers are looking for power supplies with increased diagnostic/monitoring ability," says Garrick. "The application becomes more robust when a power supply can report when its connected field devices are drawing too much current, while the integrity of the DC bus is still intact.

"For example, if the system is designed for 10 amps, it's become a reasonable expectation for the power supply to provide a signal to the process controller when the load starts to draw more than 10 amps. This signal is an early warning indication that the load is drawing too much current, and maintenance should be scheduled. When this early warning signal is received, the process controller knows the process is still running at the proper voltage at a current beyond the nominal rating of the supply. The reason for this could be a field device, such as a pump, that's getting old and requires service."

Also Read "Power Distribution:  Bring Steady, Smart Power"

If this hypothetical application continues to draw more and more current, Garrick explains, then its power supply voltage will eventually start to drop (load down). "The process controller should expect to receive a second indication when the voltage has dropped 10% down from the adjusted/required application voltage," he adds. "At 10% down in voltage, the application should be tolerant, and continue to maintain the process, but this second indication is the final warning. Any further reduction in voltage will threaten the fidelity of the process. With the reception of the second warning, maintenance must be considered. Depending on what's at stake with the application, an organized safe shutdown or an acceptable idling point should be considered."

Garrick adds that global process applications must consider various other dynamics to meet all requirements for power supply installation, and these firms will standardize on power supplies that meet these needs. "Approvals for hazardous location are the first step to determine the suitability of a power supply to be applied anywhere in the world," he explains. "Power supplies listed for use in Class I Division 2, ATEX and IEC Ex suit the need for most installations worldwide. Temperature is the next consideration for an application. Temperature can vary greatly depending on the location of the installation. Global process integration companies need power supplies rated for -40 °C to 70 °C to meet their design specifications.

"Finally, the last important, but commonly overlooked factor is choosing a power supply with printed circuit boards (PCBs) that have been dipped in conformal coating. Conformal-coated power supplies provide resistance from moisture, such as salt spray, corrosive gases, conductive dust and other contaminants that could influence the life of the power supply. Please know that all coated supplies are not created equal. Techniques range from hand painting, spray and dip coating the PCB. Perfect coverage can only be obtained by dipping the entire PCB in conformation coating. When evaluating the supplies, the extent of the coverage can be determined by analyzing the PCBs under an ultraviolet light source."